1. Technical Field
The present invention relates generally to a pneumatic vehicle tire. In particular, the present invention relates to an improved flipper structure in the bead area of the tire.
2. Description of the Prior Art
A pneumatic vehicle tire typically includes a pair of axially spaced apart beads. Each bead is substantially inextensible in the circumferential and diametral directions. A bead filler extends radially outwardly from a respective bead. At least one carcass ply extends between the beads. The carcass ply has axially opposite end portions, each of which is turned up around a respective bead and secured thereto. Tread rubber and sidewall rubber is located outwardly of the carcass ply. If the tire is a radial type of pneumatic tire, a belt package is provided and located between the carcass ply and the tread of the tire.
It is known that the automotive industry continually seeks to improve the fuel economy of each vehicle manufactured. In fact, many national governments throughout the world either have or are proposing mandated minimum fuel economy standards. In the United States of America, for example, minimum standards for corporate average fuel economy are constantly increasing. One way that the vehicle manufacturers increase their respective corporate average fuel economy is to reduce the overall resistance of the vehicle to movement.
A portion of the energy to move a vehicle is used to overcome the resistance of the tire to rolling at recommended operating conditions. It is known that approximately one third of a percent reduction in fuel economy is realized in a one percent reduction in rolling resistance for passenger car tires. The rolling resistance of a tire can be decreased by improved tire designs and by making vehicle operational changes. For example, a higher inflation pressure is an operational change that can decrease the rolling resistance of the tire. A design change may be the introduction of new materials having a low hysteresis property. One area of the tire that contributes a substantial amount to the rolling resistance of the tire is the bead area. Structural design changes in the bead area can improve rolling resistance of the tire by reducing stress and strain in the bead area. However, structural changes in the bead area of the tire which reduce the stresses and strains (often through increases in the rigidity of the bead structure) typically tend to decrease ride comfort characteristics. Structural changes in the bead area of the tire have included a variety of approaches.
For example, U.S. Pat. No. 4,711,285 discloses a bead filler having an anisotropic elasticity. The anisotropic elasticity is accomplished by incorporating short fibers of a thermoplastic material into the rubber composition of the bead filler. The short fibers are oriented in the longitudinal direction during an extrusion operation used to produce the bead filler. When the bead filler is formed radially outward of the bead, the short fibers become oriented in a circumferential direction of the assembled tire.
It is known to provide a flipper surrounding the bead and bead filler made from a square woven cloth. The cloth is typically made of a textile material in which each fiber (thread) has a generally round cross-section. When this known flipper is cured in the tire, the stiffness of the filaments are essentially the same when taken in any direction.
Examples of other flippers are found in U.S. Pat. Nos. 2,493,614 and 3,253,639 which disclose disadvantages associated with the flippers. In U.S. Pat. No. 2,493,614 the ride comfort of a tire is decreased by limiting the "yieldingness" in the sidewalls of the tires. In U.S. Pat. No. 3,253,639 radial and circumferential deformations of the tire are disclosed. The deformations result in shearing stresses during normal operation of the tire. Circumferential deformations create relatively high shearing stresses between plies and within a ply in the areas of the tire where the flippers overlap the radial carcass ply cords. Limits on the radial turnup extent of the carcass ply cords around the beads are made to locate the ends of the ply where radial deformations of the tire are relatively small. The ends of carcass ply which are turned up around the beads generally do not extend beyond one third of the interior height of the tire measured from the bead to the interior surface of the tire at the crown.
Stresses that reduce energy losses in the bead assembly are frequently accompanied by strains that give less ride comfort. A balance between stresses and strains in the tire is desirable. A balanced design for a reinforced bead assembly of a tire has stress characteristics for increased endurance and reduced energy loss and strain characteristics for adequate ride comfort. Thus, there is a need for a new tire which has decreased rolling resistance without increasing vehicle ride harshness.
An objective of this invention is to provide reinforcement of each bead assembly to help protect the beads from exterior damage and to provide a better balance between stress and strain characteristics in the bead area than prior art tires. The reinforcement shall be designed to have an improved hysteresis property. This objective is to improve the rolling resistance of the tire. Another objective of this invention is to limit the radial extent of the flipper, as well as the carcass ply turnup, to maintain optimum circumferential and radial stiffness properties of the tire. This objective is associated with maintaining vehicle ride comfort.